The European Space Agency received the message shortly after 1 p.m. EST from the Rosetta spacecraft which is reportedly some 500 million miles away.

In 2011, the Rosetta spacecraft was placed in hibernation to conserve its energy as it travels to meet comet 67P/Churyumov-Gerasimenko. If all goes as planned, the probe will rendezvous with the comet in the coming months and drop a lander onto its icy surface in November, the Associated Press reported.

Prior to receiving the message, scientists at the European Space Agency were unsure of the spacecraft’s status.

"There is a possibility that we're not going to hear anything. Two-and-a-half years are a long time," Paolo Ferri, head of mission operations at the European Space Agency, said prior to the Rosetta Spacecraft’s awakening. "We've taken all possible precautions for this not to happen but of course we cannot exclude that problems may have happened."

The mood immediately changed once the signal came in.

"I think it's been the longest hour of my life," Andrea Accomazzo, the spacecraft's operations manager at ESA's mission control room in Darmstadt, Germany, told reporters. "Now we have it back."

The signal was received about 45 minutes after it was sent by the probe. The time lapse is due to the distance between the Rosetta spacecraft and the Earth.

If successful, the probe will be the first time scientists have put a lander on a comet, which will then collect and analyze samples from the surface of the icy space rock.

Distinguishable from asteroids by their tail, comets, which are roughly the size of a small town, are primordial bodies comprised of the same fundamental building blocks that were responsible for the formation of planets billions of years ago.

In 2001, NASA managed to land a probe on an asteroid; however comets, due to their volatility, pose a significantly greater risk to spacecraft because of their constant release of dust and gas.

Four years later, NASA launched its Deep Impact mission through which a spacecraft fired a projectile into a comet so that scientists could study the resulting plume of matter.

The Rosetta spacecraft, a comet-chasing probe that had been in hibernation for nearly three years, awoke Monday and sent its first signal back to Earth in the form of multilingual tweets that said "Hello World!"